1. Field of the Invention
The present invention relates to a process for prearing a varnish for a printing ink using an acid sludge which previously was a source of pollution of the raw material.
2. Description of the Prior Art
Two processes for the preparation of mineral lubricating oils from crude oil are known. One is a hydrogenation-furfural extraction process and the other is a sulfuric acid treatment. In the sulfuric acid treatment, it is possible to prepare lubricating oils having high stability by sulfonation, sulfation, or dissolution in sulfuric acid and an extraction of unsaturated hydrocarbons, resinous matter, asphalts and amines which are in petroleum fractions. The by-product of the sulfuric acid treatment is referred as an acid sludge, has strong acidity and contains relatively large amounts of oil components. As a result, it is difficult to effectively utilize this sludge and it is also difficult to dispose of. Typically, the acid sludge is disposed of by neutralization with limestone or by burning.